Twenty patients will be randomily assigned to convert overnight (10 pts) or over six days (10 pts). Side effects will be formally evaluated by the UKU side effect rating scal which will be done 7 days before conversion (day -7), the day of conversion (day 0)and then at the start of days +2, +7 and +14. This investigator conducting the evaluation will be blinded to the conversion status of the patient. Secondary measures to be obtained will be a Quality of Life measure (QOLIE-89) on Day 0 and +14. Plasma samples will be obtained on Day 0 and +14 before dosing for total and free valproic blood level.